A known sheet feeder includes a sheet supply tray, a separation roller, a separation pad, and a sheet pressing plate. The sheet supply tray is configured to store a stack of recording sheets. The separation roller is disposed to rotate in contact with an uppermost sheet in the sheet supply tray and configured to apply a feeding force to the sheet. The separation pad is disposed facing the separation roller and configured to contact a sheet from an opposite side from the separation roller and provide a resistance with the sheet. The sheet pressing plate is disposed inside the sheet supply tray. The sheet pressing plate is pivotally supported at one end remote from the separation pad such that the sheet pressing plate is vertically movable at the other end closest to the separation pad as the number of recording sheets stored in the sheet supply tray decreases.
However, when the sheet pressing plate ascends, a friction surface of the separation pad that contacts the recording sheet and an imaginary plane including the sheet pressing plate forms a small angle, and the friction surface and the imaginary plane become close to parallel to each other.
At this time, a recording sheet is fed from the sheet supply tray to the separation pad in a direction parallel to the sheet pressing plate and contacts the friction surface of the separation pad. When the sheet pressing plate ascends and the friction surface and the imaginary plane become close to parallel, a frictional force generated between the friction surface of the separation pad and the recording sheet becomes small.
Thus, when the sheet pressing plate ascends, the frictional force between the friction surface of the separation pad and the recording sheet becomes small and a sufficient resistance may not be applied to the recording sheet. As a result, multi-feeding where multiple recording sheets are erroneously fed at a specific time may occur.